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Polyploid plants often exhibit enhanced stress tolerance. Switchgrass is a perennial rhizomatous bunchgrass that is considered ideal for cultivation in marginal lands, including sites with saline soil. In this study, we investigated the physiological responses and transcriptome changes in the octoploid and tetraploid of switchgrass (Panicum virgatum L. 'Alamo') under salt stress. We found that autoploid 8× switchgrass had enhanced salt tolerance compared with the amphidiploid 4× precursor, as indicated by physiological and phenotypic traits. Octoploids had increased salt tolerance by significant changes to the osmoregulatory and antioxidant systems. The salt-treated 8× Alamo plants showed greater potassium (K+) accumulation and an increase in the K+/Na+ ratio. Root transcriptome analysis for octoploid and tetraploid plants with or without salt stress revealed that 302 upregulated and 546 downregulated differentially expressed genes were enriched in genes involved in plant hormone signal transduction pathways and were specifically associated with the auxin, cytokinin, abscisic acid, and ethylene pathways. Weighted gene co-expression network analysis (WGCNA) detected four significant salt stress-related modules. This study explored the changes in the osmoregulatory system, inorganic ions, antioxidant enzyme system, and the root transcriptome in response to salt stress in 8× and 4× Alamo switchgrass. The results enhance knowledge of the salt tolerance of artificially induced homologous polyploid plants and provide experimental and sequencing data to aid research on the short-term adaptability and breeding of salt-tolerant biofuel plants. [ABSTRACT FROM AUTHOR]

Perennial biomass cropping systems are generally considered to be more environmentally friendly and sustainable compared to annual cropping systems, largely due to reduced input requirements. Nitrogen fertilizer is, by far, the most expensive input into perennial grass-based bioenergy systems, demanding research efforts focused on increasing nitrogen-use efficiency of biomass crops. The purpose of this study was to identify genetic variability for nitrogen-use efficiency and to determine if it is possible to identify genotypes that can produce high biomass yields without nitrogen fertilizer applications. A total of 83 half-sib families were grown in replicated paired plots on two different marginal soils. Paired plots consisted of 0 or 100 kg N ha−1, allowing for a highly precise computation of the direct impact of nitrogen fertilizer. There were strong genotype x location interactions, as well as strong genotype x nitrogen rate interactions at one of the two locations. For both locations, the direct response to nitrogen fertilization on biomass yield was strongly and negatively related to biomass yield without nitrogen fertilizer. Many families had high yield without fertilizer application, but also had non-significant responses to the fertilizer application. However, the ranking of these families was highly inconsistent between the two locations and soil types. These results suggested that certain families were likely responding to favorable associations with nitrogen-fixing microbes and that those associations were inconsistent between the two soil types. Development of new switchgrass cultivars that can form associations with nitrogen-fixing microbes should be conducted under conditions that favor such associations, strictly avoiding application of nitrogen fertilizers. [ABSTRACT FROM AUTHOR]

Perennial grasses are candidates for biomass cropping systems that are focused on providing a wide range of ecosystem services in addition to sustainable bioenergy production. Switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman) are two of the dominant grasses of the tallgrass prairie and both are candidates for development of multifunctional diverse production systems. Breeding programs for both species are aimed at increasing biomass yield as a mechanism of improving economic sustainability without increasing production costs. The objective of this study was to determine if long-term selection for increased biomass yield in these two species has had any adverse impacts on biomass quality, or the ability to convert biomass into bioenergy. Check cultivars and improved breeding populations of both species were evaluated for a wide range of biomass quality traits at 13 locations in the North Central and Northeastern USA, and a subset of these populations were also subjected to more intensive and detailed fermentation analyses. In general, lignin and ferulates either remained constant or decreased following selection for increased biomass yield in the various genetic pedigrees. These changes resulted in some increases in predicted ethanol production and in vitro digestibility. The prediction of increased digestibility was confirmed by higher glucose release by pretreatment and deconstruction of an advanced lowland population. However, bioreactor fermentations with two different biofuel-producing microbes showed no differences in ethanol production. Overall, these studies indicated that the improved switchgrass and big bluestem populations had greater biomass yields without significantly reducing biomass quality or conversion efficiency into ethanol, suggesting that selection can achieve increases in biomass productivity while maintaining consistent biomass quality. [ABSTRACT FROM AUTHOR]

The selection of non-food crops for bioenergy production in limiting environments is a priority for energy security and climate change mitigation. Therefore, more studies are needed on the interactions between species and environmental factors in specific sites which allows their selection for biomass production. The objective of this work is to study the impact of drought on the morpho-physiological parameters of perennial rhizomatous grasses Panicum virgatum L., Miscanthus × giganteus, and Arundo donax L. in the Mediterranean environment. Plants were grown on field and trials were carried out under support-irrigation and rainfed conditions during two consecutive years. Morpho-physiological parameters were measured in May, June and August, and dry biomass at the end of the experiment. Under rainfed conditions, A. donax presented the highest photosynthesis rate (25, 15 and 10 CO2 m−2 s−1), relative water content (85–90%), and dry biomass (~4500 g plant−1) compared with P. virgatum (20, 5 and 5 CO2 m−2 s−1, 65–85% RWC and ~1400 g plant−1) and Miscanthus (18, 4 and 0 CO2 m−2 s−1, 80–10% RWC and ~260 g plant−1). It is concluded that A. donax would be the best perennial rhizomatous grass to be used as bioenergy crop under Mediterranean conditions. [ABSTRACT FROM AUTHOR]

Polyploid plants often exhibit enhanced stress tolerance. Switchgrass is a perennial rhizomatous bunchgrass that is considered ideal for cultivation in marginal lands, including sites with saline soil. In this study, we investigated the physiological responses and transcriptome changes in the octoploid and tetraploid of switchgrass (Panicum virgatum L. ‘Alamo’) under salt stress. We found that autoploid 8× switchgrass had enhanced salt tolerance compared with the amphidiploid 4× precursor, as indicated by physiological and phenotypic traits. Octoploids had increased salt tolerance by significant changes to the osmoregulatory and antioxidant systems. The salt-treated 8× Alamo plants showed greater potassium (K+) accumulation and an increase in the K+/Na+ ratio. Root transcriptome analysis for octoploid and tetraploid plants with or without salt stress revealed that 302 upregulated and 546 downregulated differentially expressed genes were enriched in genes involved in plant hormone signal transduction pathways and were specifically associated with the auxin, cytokinin, abscisic acid, and ethylene pathways. Weighted gene co-expression network analysis (WGCNA) detected four significant salt stress-related modules. This study explored the changes in the osmoregulatory system, inorganic ions, antioxidant enzyme system, and the root transcriptome in response to salt stress in 8× and 4× Alamo switchgrass. The results enhance knowledge of the salt tolerance of artificially induced homologous polyploid plants and provide experimental and sequencing data to aid research on the short-term adaptability and breeding of salt-tolerant biofuel plants.

The selection of non-food crops for bioenergy production in limiting environments is a priority for energy security and climate change mitigation. Therefore, more studies are needed on the interactions between species and environmental factors in specific sites which allows their selection for biomass production. The objective of this work is to study the impact of drought on the morpho-physiological parameters of perennial rhizomatous grasses Panicum virgatum L., Miscanthus × giganteus, and Arundo donax L. in the Mediterranean environment. Plants were grown on field and trials were carried out under support-irrigation and rainfed conditions during two consecutive years. Morpho-physiological parameters were measured in May, June and August, and dry biomass at the end of the experiment. Under rainfed conditions, A. donax presented the highest photosynthesis rate (25, 15 and 10 CO2 m−2 s−1), relative water content (85–90%), and dry biomass (~4500 g plant−1) compared with P. virgatum (20, 5 and 5 CO2 m−2 s−1, 65–85% RWC and ~1400 g plant−1) and Miscanthus (18, 4 and 0 CO2 m−2 s−1, 80–10% RWC and ~260 g plant−1). It is concluded that A. donax would be the best perennial rhizomatous grass to be used as bioenergy crop under Mediterranean conditions.

Abstract Background Newly formed polyploids may experience short-term adaptative changes in their genome that may enhance the resistance of plants to stress. Considering the increasingly serious effects of drought on biofuel plants, whole genome duplication (WGD) may be an efficient way to proceed with drought resistant breeding. However, the molecular mechanism of drought response before/after WGD remains largely unclear. Result We found that autoploid switchgrass (Panicum virgatum L.) 8X Alamo had higher drought tolerance than its parent amphidiploid 4X Alamo using physiological tests. RNA and microRNA sequencing at different time points during drought were then conducted on 8X Alamo and 4X Alamo switchgrass. The specific differentially expressed transcripts (DETs) that related to drought stress (DS) in 8X Alamo were enriched in ribonucleoside and ribonucleotide binding, while the drought-related DETs in 4X Alamo were enriched in structural molecule activity. Ploidy-related DETs were primarily associated with signal transduction mechanisms. Weighted gene co-expression network analysis (WGCNA) detected three significant DS-related modules, and their DETs were primarily enriched in biosynthesis process and photosynthesis. A total of 26 differentially expressed microRNAs (DEmiRs) were detected, and among them, sbi-microRNA 399b was only expressed in 8X Alamo. The targets of microRNAs that were responded to polyploidization and drought stress all contained cytochrome P450 and superoxide dismutase genes. Conclusions This study explored the drought response of 8X and 4X Alamo switchgrass on both physiological and transcriptional levels, and provided experimental and sequencing data basis for a short-term adaptability study and drought-resistant biofuel plant breeding.

Abstract Background Understanding the DNA methylome and its relationship with non-coding RNAs, including microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), is essential for elucidating the molecular mechanisms underlying key biological processes in plants. Few studies have examined the functional roles of the DNA methylome in grass species with highly heterozygous polyploid genomes. Results We performed genome-wide DNA methylation profiling in the tetraploid switchgrass (Panicum virgatum L.) cultivar ‘Alamo’ using bisulfite sequencing. Single-base-resolution methylation patterns were observed in switchgrass leaf and root tissues, which allowed for characterization of the relationship between DNA methylation and mRNA, miRNA, and lncRNA populations. The results of this study revealed that siRNAs positively regulate DNA methylation of the mCHH sites surrounding genes, and that DNA methylation interferes with gene and lncRNA expression in switchgrass. Ninety-six genes covered by differentially methylated regions (DMRs) were annotated by GO analysis as being involved in stimulus-related processes. Functionally, 82% (79/96) of these genes were found to be hypomethylated in switchgrass root tissue. Sequencing analysis of lncRNAs identified two lncRNAs that are potential precursors of miRNAs, which are predicted to target genes that function in cellulose biosynthesis, stress regulation, and stem and root development. Conclusions This study characterized the DNA methylome in switchgrass and elucidated its relevance to gene and non-coding RNAs. These results provide valuable genomic resources and references that will aid further epigenetic research in this important biofuel crop.

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Development of switchgrass (Panicum virgatum L.) as a sustainable biomass crop for conversion to bioenergy requires substantial increases in biomass yield. Because switchgrass is highly photoperiodic, one approach toward this goal is to collect germplasm populations from the Southern USA, then screen and select them in northern environments where they represent a delay in flowering time of up to 6 weeks compared with local ecotypes. This delay in flowering has been linked to increases in biomass yield of up to 50%. The objective of this study was to conduct and evaluate selection progress for winter survivorship in 14 southern lowland populations of switchgrass. The populations originated from USDA Plant Hardiness Zones (PHZ) 7 or 8 (mean annual extreme minimum temperature = − 12.2 °C) and the selection and evaluation were conducted in PHZ 4 or 5 (mean annual extreme minimum temperature = − 28.8 °C). Seven of the 14 populations responded to selection, with increases in winter survivorship and/or biomass yield across four evaluation locations. Winter survivorship and biomass yield were highly correlated with each other, so that increases in survivorship usually translated to increases in biomass yield. The top-ranked population represented the third cycle of selection within the cultivar Kanlow, indicating that the greatest gains from selection represented longer-term efforts than a single generation of field-based selection. This study verified that alleles for winter survivorship and plants capable of surviving in PHZ 4 or 5 can be found across a broad geographic area in the Southern USA, albeit at very low frequencies in most populations. [ABSTRACT FROM AUTHOR]

Development of perennial biomass cropping systems is focused on maximizing biomass yield with minimum inputs, particularly nitrogen (N) fertilizer. Historical breeding efforts have focused on increasing biomass yield but have ignored N-use efficiency. The purpose of this study was to quantify the increased N demand associated with realized gains in biomass yield from big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) breeding programs. Nitrogen demand was highly variable across locations and years, ranging from − 1.7 to + 6.8 kg N Mg−1 DM, with an average of 2.2 kg N Mg−1 DM. Increases in N demand were closely associated with realized gains in biomass yield and were observed for all types of switchgrass (upland, lowland, and hybrid) as well as for big bluestem. Attenuation of these responses will require alternative breeding schemes that are focused on evaluation of switchgrass genotypes and progeny under low-N conditions and include a high-throughput tissue N analysis as a component of future selection criteria, designed to develop new cultivars with high biomass yield and low tissue N. [ABSTRACT FROM AUTHOR]

Purpose. To define morphological peculiarities of the different types of shoots of switch grass (Panicum virgatum L.) in the context of introduction in the Right-Bank Forest-Steppe and Polissia zones of Ukraine. Methods. Morpho-physiological and ontogenetic analysis, morphometric technique, statistical evaluation. Results. It was found that P. virgatum plants were producing the following types of shoots: vegetative-generative short or long rhizomatous ones (they appeared as in the underground part of a maternal shoot in «the area of shortened internodes» and in the base of its aboveground part); vegetative underground and aboveground ones (they are forming both in the axils of scales of the underground part of a maternal shoot and in the axils of cauline leaves); generative aboveground shoots (borne in the axil of cauline leaves). Morphological parameters and features of morphogenesis of reproduction, resting and secondary buds have been described. Conclusions. During flowering phase of maternal shoot, P. virgatum reproduction buds were on the organogenesis phase I–II, their bursting occured after maternal shoot has flowered. The correlation of internodes length, leave blades and sheaths has been established. The maximum values of the above parameters were observed in the middle part of the prefloral zone of the stem. In the context of introduction, panicle earing came in the third decade of July, flowering began in the first decade of August. It was revealed that complete flowers are bloomed faster than the staminate ones.

Main conclusion: Rhizosheath comprises soil that adheres firmly to roots. In this study, two ecotypes of switchgrass with different rhizosheath sizes after drought stress were analyzed which showed metabolic differences under drought conditions. The rhizosheath comprises soil that adheres firmly to roots by a combination of root hairs and mucilage and may aid in root growth under soil drying. The aim of this work is to reveal the potential metabolites involved in rhizosheath formation under drought stress conditions. Panicum virgatum L. (switchgrass), which belongs to the Poaceae family, is an important biofuel and fodder crop in drought areas. Five switchgrass ecotypes (cv. Alamo, cv. Blackwake, cv. Summer, cv. Cave-in-Rock and cv. Kanlow) have a broad range of rhizosheath weight under drought conditions. For two selected ecotypes with contrast rhizosheath weight (cv. Alamo and cv. Kanlow), root hair length and density, lateral root number, root morphological parameters were measured, and real-time qRT-PCR was performed. Gas chromatography mass spectrophotometry (GC–MS) was used to determine the primary metabolites in the shoots and roots of selected ecotypes under drought stress conditions. The change trends of root hair length and density, lateral root number and related gene expression were consistent with rhizosheath weight in Alamo and Kanlow under drought and watered conditions. For root morphological parameters, Alamo grew deeper than Kanlow, while Kanlow exhibited higher values for other parameters. In this study, the levels of amino acids, sugars and organic acids were significantly changed in response to drought stress in two switchgrass ecotypes. Several metabolites including amino acids (arginine, isoleucine, methionine and cysteine) and sugars (kestose, raffinose, fructose, fucose, sorbose and xylose) in the large soil-sheathed roots of Alamo and Kanlow were significantly increased compared to small or no soil-sheathed roots of Alamo and Kanlow. Difference in rhizosheath size is reflected in the plant internal metabolites under drought stress conditions. Additionally, our results highlight the importance of using metabolite profiling and provide a better understanding of rhizosheath formation at the cellular level. [ABSTRACT FROM AUTHOR]

Summary: Ferulate 5‐hydroxylase (F5H) catalyses the hydroxylation of coniferyl alcohol and coniferaldehyde for the biosynthesis of syringyl (S) lignin in angiosperms. However, the coordinated effects of F5H with caffeic acid O‐methyltransferase (COMT) on the metabolic flux towards S units are largely unknown. We concomitantly regulated F5H expression in COMT‐down‐regulated transgenic switchgrass (Panicum virgatum L.) lines and studied the coordination of F5H and COMT in lignin biosynthesis. Down‐regulation of F5H in COMT‐RNAi transgenic switchgrass plants further impeded S lignin biosynthesis and, consequently, increased guaiacyl (G) units and reduced 5‐OH G units. Conversely, overexpression of F5H in COMT‐RNAi transgenic plants reduced G units and increased 5‐OH units, whereas the deficiency of S lignin biosynthesis was partially compensated or fully restored, depending on the extent of COMT down‐regulation in switchgrass. Moreover, simultaneous regulation of F5H and COMT expression had different effects on cell wall digestibility of switchgrass without biomass loss. Our results indicate that up‐regulation and down‐regulation of F5H expression, respectively, have antagonistic and synergistic effects on the reduction in S lignin resulting from COMT suppression. The coordinated effects between lignin genes should be taken into account in future studies aimed at cell wall bioengineering. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass is one of the dominant renewable energy resources suited for the production of sustainable biofuels and other energy purposes. This study was focused on weed management strategies that can improve the establishment of six lignocellulosic crops. The studied crops included: giant miscanthus, switchgrass, giant reed, cardoon, sweet sorghum, and kenaf. Delayed planting, increased planting densities, and mulching techniques can suppress weeds in giant miscanthus. Weed competition is detrimental for switchgrass establishment. Seedbed preparation and cultivar selection can determine its ability to compete with weeds. Giant reed is unlikely to get outcompeted by weeds, and any weed control operation is required only for the first growing season. Competitive cultivars and increased seeding rates maximize the competitiveness of cardoon against weeds. Several cultural practices can be used for non-chemical weed management in sweet sorghum and kenaf. For all crops, pre-emergence herbicides can be applied. The available safe post-emergence herbicides are limited. Mechanical weed control during crucial growth stages can provide solutions for sweet sorghum, kenaf, and perennial grasses. Further research is required to develop effective weed management strategies, with emphasis on cultural practices, that can improve the establishment of these prominent lignocellulosic crops.

Switchgrass (Panicum virgatum L.) originates from North America as one of the species found in the highland prairie. As an energy crop, it has great potential and is widely used in developed countries. It can be used for erosion prevention (due to a strong root system), bird feeding, and landscape architectural purposes (as an ornamental species). In low-quality soils, switchgrass provides protection against erosion and grass cover for grazing. In this paper, we examined the biomass quality of 14 genotypes of switchgrass for animal feed. The cutting of switchgrass was performed on the same day, including all the genotypes examined (mostly in the pre-flowering stage, or at the beginning of flowering). The following parameters of switchgrass biomass quality were analysed: crude protein, crude cellulose, fat content, ash content, NFE, ADF and NDF. In Serbia, this species can be a component of grass mixtures used in lesser quality soils and under dry agroecological conditions.

Switchgrass is native to the tallgrass prairie of North America. It is self-incompatible and has varied ploidy levels from diploid (2x) to dodecaploid (12x) with tetraploid and octoploid being the most common. The high yielding potential and the ability to grow well in marginal lands make switchgrass an ideal species as a dedicated biomass producer for lignocellulosic ethanol production. Genetic transformation is an important tool for studying gene function and for germplasm improvement in switchgrass, the genome of which has been sequenced recently. This paper intends to provide a comprehensive review on plant regeneration and genetic transformation in switchgrass. We first reviewed the effect of explants, basal medium and plant growth regulators on plant regeneration in switchgrass, which is a prerequisite for genetic transformation. We then reviewed the progresses on genetic transformation with either the biolistic or Agrobacterium-mediated method in switchgrass, and discussed various techniques employed to improve the transformation efficiency. Finally we reviewed the recent progresses on the use of genetic transformation in improving biomass quality such as the reduction of lignin, and in increasing biomass yield in switchgrass. We also provided a future perspective on the use of new genome editing technologies in switchgrass and its potential impact on regulatory processes.

Cellulosic biofuels are an important source of renewable biomass within the alternative energy portfolio. Switchgrass (Panicum virgatum L.), a perennial C4 grass native to North America, is widely studied as a biofuel feedstock for its consistently high yields and minimal input requirements. The influences of precipitation amount and temporal variability on the fertilizer response of switchgrass productivity are not fully understood. Moreover, global climate models predict changes in rainfall patterns towards lower and increasingly variable soil water availability in several productive areas worldwide, which may impact net primary production of biofuel crops. We conducted a meta-analysis of aboveground net primary production of switchgrass from 48 publications encompassing 82 different locations, 11 soil types, 52 switchgrass cultivars, fertilizer inputs between 0 to 896 kg N ha−1 year−1, and 1 to 6 years of annual productivity measures repeated on the same stand. Productivity of the lowland ecotype doubled with N rates > 131 kg N ha−1 year−1, but upland ecotype productivity increased only by 50%. Results showed an optimum N rate of 30 to 60 kg N ha−1 year−1 for both ecotypes, after which biomass gain per unit of N added decreased. Growing season precipitation (GSPPT) and inter-annual precipitation variability (inter-PPTvar) affected both ecotypes similarly. Long-term mean annual precipitation (MAP) differentially affected lowland and upland productivity, depending on the N level. Productivity responses to MAP and GSPPT were similar for both upland and lowland ecotypes at none or low N rates. When N increased beyond 60 kg N ha−1 year−1, lowland cultivars had a greater growth response to MAP than uplands. Productivity increased with increasing GSPPT and MAP and had a positive linear response to MAP ranging from 600 to 1200 mm year−1. One third of the variability in switchgrass production was accounted for by inter-PPTvar. After accounting for MAP, sites with higher inter-PPTvar had lower switchgrass productivity than sites with lower inter-PPTvar. Increased inter-annual variation in precipitation reduced production of both ecotypes. Predicted changes in the amount and timing of precipitation thus likely will exert greater influence on production of upland than lowland ecotypes of switchgrass. [ABSTRACT FROM AUTHOR]

Switchgrass ( Panicum virgatum L.) adapts to a wide range of environments. It has been successfully planted in a semiarid region of China’s Loess Plateau as a valuable forage species for restoring vegetation of grassland. However, growth performance of switchgrass needs to be further evaluated after establishment. Relationships between switchgrass growth and outcomes of weed control in terms of nitrogen (N) supply are especially not well understood. Field studies were conducted in 5-year and 8-year switchgrass stands at two semiarid sites. Nitrogen fertilizer (ammonium nitrate) was supplied at rates equivalent to 0 kg N ha −1 , 120 kg N ha −1 , and 240 kg N ha −1 in switchgrass stands consisted of three upland cultivars (Blackwell, Cave-in-Rock and Pathfinder). A split-plot experimental design was employed with 3 replications. Switchgrass and its associated weed growth were assayed. Switchgrass growth and production were generally improved with N rate increasing, although there were some cultivar and location variations. Cave-in-Rock switchgrass had advantages over other cultivars in plant height, biomass and seed production, as well as weed control effect. The N rate of 120 kg N ha −1 was suggested for seed production of switchgrass. In switchgrass stands, weed density was increased with N rate increasing, whereas biomass was decreased. Weed density was positively related with switchgrass height ( P <  0.05), whereas weed biomass were negatively regressed with switchgrass height, tiller density and biomass ( P <  0.05). These results demonstrate that N supply is necessary for established switchgrass stands, because there are production and weed control benefits from fertilizing switchgrass with N supply rate of 240 kg N ha −1 . Practical implications of this study are that culture practices, such as cultivars selection, N management and integrated weed management strategy will contribute to the productivity of established switchgrass stands in the semiarid Loess Plateau. [ABSTRACT FROM AUTHOR]

Sustainable development of the bioenergy industry will depend upon the amount and quality of bioenergy feedstock produced. Switchgrass (Panicum virgatum L.) is a model lignocellulosic bioenergy crop but critical information is lacking for improved management, growth, and development simulation model calibration. A field study was conducted near Ames, IA during 2012-2013 with the objective to evaluate upland ("Cave-in-Rock", 'Trailblazer' and 'Blackwell') and lowland ("Kanlow" and "Alamo") switchgrass ecotypes for harvest timing on morphology (i.e., phenology, leaf area index (LAI), and biomass yield). The experiment used a randomized complete block design, with three upland and two lowland varieties harvested at six dates annually. In both years, delaying harvest to later maturity increased biomass yield; lowland cultivars produced greater biomass yield (6.15 tons ha-1 Lowland ecotypes had delayed reproductive development compared with upland ecotypes. At the end of both growing seasons, upland ecotypes had greater mean stage count (MSC) than lowland ecotypes. "Cave-in-Rock" had greatest MSC and LAI, but did not produce the greatest biomass. Relationships were nonlinear between MSC and biomass yield, with significant cultivar--year interaction. The relationship between biomass yield and MSC will be useful for improving switchgrass, including cultivar selection, fertilizer application, and optimum harvest time. [ABSTRACT FROM AUTHOR]

The bioenergy mandate under Energy Independence and Security Act (EISA 2007) will result in large scale land-use changes in the US if it is ever fully realized. Energy crops such as switchgrass (Panicum virgatum) and miscanthus (Miscanthus X giganteus) can grow well throughout the continental United States; however, most studies on the water quality impacts of land-use change from bioenergy policy are based in the Midwest. Insufficient research has been conducted to determine whether the results from the Midwest are applicable to other regions in the United States. This study compares water quality impacts of converting from corn to switchgrass in the Midwest (Upper Cedar watershed) and Southeast (Lumber watershed) with nitrogen loading to surface water as a proxy metric for overall water quality impacts using the Soil and Water Assessment Tool (SWAT). The analysis shows that the fraction of nitrogen runoff compared to the fertilizer applied is 36% in Upper Cedar as compared to 6% in Lumber. Existing management practices like tile-drainage and land-cover like riparian wetlands contribute to this difference in the baseline nitrate export from each watershed. The potential reduction in nitrogen loading per potential liter of ethanol to surface waters, which account for both nitrate export and productivities, from the baseline corn-soy to switchgrass is about 40% for the Upper Cedar watershed and around 80% for the Lumber watershed. Although, the trend in reduction is similar in both watersheds, this study shows that results extrapolated from the Midwest may not be representative of other bioenergy producing regions. [ABSTRACT FROM AUTHOR]

Ideal bioenergy feedstocks are low in nutrients that act as anti-quality factors during conversion processes. Research has shown that delaying harvest of temperate perennial grasses until late winter reduces nutrient content, primarily due to end-season resorption, but also indicates a role for foliar nutrient leaching. While end-season resorption has been estimated, foliar nutrient leaching has not, and is a factor that could refine harvest recommendations. Additionally, establishing a baseline of mineral loss during switchgrass senescence will improve our understanding of leaf-level nutrient resorption. Therefore, we applied simulated rainfall to replicated ( n = 5) plots within a previously established switchgrass stand to determine if heavy precipitation can induce nutrient leaching in senescing, unharvested foliage. Hour-long simulated rainfalls of ∼120 mm were applied every 2 weeks from early September to a killing frost in 2014 and 2015. Leaf samples were taken from the upper and lower canopy before and after simulated rainfalls and from no-rain controls and analyzed for elemental N, P, K, S, Mg, and Ca. Nutrient resorption estimates ranged from 33 to 82% in control plots. Comparison of rainfall plots to controls indicated that lower canopy leaves, upon reaching ≥50% senescence, were slightly susceptible to foliar nutrient leaching, with losses ranging from 0.3 to 2.8 g kg dry matter for K, P, and Mg. Nitrogen, Ca, and S were not susceptible to foliar leaching. Although statistically significant ( P ≤ 0.05), these values suggested that foliar leaching was not a strong driver of nutrient loss during senescence. [ABSTRACT FROM AUTHOR]

Switchgrass is one of the most promising energy crops and only recently has been employed for biofuel production. The draft genome of switchgrass was recently released; however, relatively few switchgrass genes have been functionally characterized. CENH3, the major histone protein found in centromeres, along with canonical H3 and other histones, plays an important role in maintaining genome stability and integrity. Despite their importance, the histone H3 genes of switchgrass have remained largely uninvestigated. In this study, we identified 17 putative switchgrass histone H3 genes in silico. Of these genes, 15 showed strong homology to histone H3 genes including six H3.1 genes, three H3.3 genes, four H3.3-like genes and two H3.1-like genes. The remaining two genes were found to be homologous to CENH3. RNA-seq data derived from lowland cultivar Alamo and upland cultivar Dacotah allowed us to identify SNPs in the histone H3 genes and compare their differential gene expression. Interestingly, we also found that overexpression of switchgrass histone H3 and CENH3 genes in N. benthamiana could trigger cell death of the transformed plant cells. Localization and deletion analyses of the histone H3 and CENH3 genes revealed that nuclear localization of the N-terminal tail is essential and sufficient for triggering the cell death phenotype. Our results deliver insight into the mechanisms underlying the histone-triggered cell death phenotype and provide a foundation for further studying the variations of the histone H3 and CENH3 genes in switchgrass.

The use of switchgrass (Panicum virgatum L.) as an energy crop has gained great importance in past two decades due to its high biomass yields on marginal lands with low agricultural inputs and low maintenance requirements. Information on the allocation of photosynthetically fixed C in the switchgrass-soil system is important to understand the C flow and to quantify the sequestration of C in soils. The allocation of 13C labeled photosynthates in shoot, root, soil, and in microbial biomass carbon (MBC) of rhizosphere and bulk soil of 45 days old, greenhouse grown-switchgrass was examined during 20 days 13C-CO2 pulse labeling period. The total 13C recovered in the plant-soil system varied from 79% after 1 day to 42% after 20 days of labeling. After labeling, 54%, 40%, and 6% excess 13C resided in shoot, root and soil, respectively on day 1; 27%, 61% and 11%, respectively on day 5 and 20%, 63% and 17%, respectively day 20 after labeling. The maximum incorporation of 13C from roots into the MB of rhizosphere soil occurred within the first 24 h of labeling. The excess 13C values of rhizosphere soil and rhizosphere MBC were significantly higher than excess 13C values of bulk soil and the bulk soil MBC, respectively. The proportion of excess 13C in soil as MBC declined from 92 to 15% in rhizosphere soil and from 79 to 18% in bulk soil, for 1 day and 20 days after labeling, respectively. The present study showed the effectiveness of 13C labeling to examine the fate of recently photosynthesized C in soil-plant (switchgrass) system and dynamics of MBC.

In this work, two perennial rhizomatous grasses ( Arundo donax L. (giant reed; C 3 ) and Panicum virgatum L. (switchgrass; C 4 )) considered as promising energy crops have been subjected to four different types of stress in two experiments: (i) both species were subjected to four salinity and water stress treatments [well-watered with non-saline solution (WW S−), low-watered with non-saline solution (WS S-), well-watered with saline solution (WW S+) and low-watered with saline solution (WS S+)]; and (ii) both species were subjected to three temperature and light treatments [ambient temperature and light (C), ambient temperature and darkness (AD) and cold temperature and darkness (CD)]. Photosynthetic and physiological parameters as well as biomass production were measured in these plants. It can be hypothesized that a higher photosynthesis rate (A sat ) was be observed in switchgrass as a consequence of its C 4 metabolic pathway. However, our results indicated a similar A sat at the beginning of the experiment for both species. This could be due to switchgrass being an NAD-ME C 4 type whereas giant reed has been reported as a C 3 species with a high photosynthetic rate. We showed that switchgrass seems to be more resistant to stresses such as water stress, salinity and cold than giant reed in our greenhouse conditions. [ABSTRACT FROM AUTHOR]

The objective was to determine the breakeven price for switchgrass (SG) ( Panicum virgatum L.), a mix of big bluestem ( Andropogon gerardii Vitman) and Indiangrass (BBIG) ( Sorghastrum nutans L. Nash), and a combination of SG and BBIG (SG/BBIG) produced under three harvest treatments. Two-harvest treatments included a forage harvest at early boot (EB) and at early seedhead (ESH) plus a biomass harvest at fall dormancy (FD). The third harvest treatment was a single biomass harvest at FD. Mixed models were used to determine if there were differences in yield, crude protein, and nutrient removal for each of the native warm-season grass (NWSG) treatments at each harvest. The EB plus FD harvest system would be preferred over the ESH plus FD harvest system for all NWSG treatments. BBIG was the only NWSG treatment with a breakeven price for biomass that decreased with an EB harvest. For all three NWSG treatments, a producer would be better off harvesting once a year for biomass than twice for forage and biomass. The cost of harvesting and replacing the nutrients for the forage harvest was greater than the revenue received from selling the forage. [ABSTRACT FROM AUTHOR]

Context: Expansion of bioenergy production is part of a global effort to reduce greenhouse gas emissions and mitigate climate change. Dedicated biomass crops will compete with other land uses as most high quality arable land is already used for agriculture, urban development, and biodiversity conservation. Objective: First, we explore the trade-offs between converting land enrolled in the U.S. Conservation Reserve Program (CRP) to switchgrass for biofuel production or preserving it for biodiversity. Next, we examine the trade-offs between agriculture, biodiversity, and biofuel across the central and eastern U.S. Methods: We compiled measures of biodiversity, agriculture, and biofuel from land cover classifications, species range maps, and mechanistic model output of switchgrass yield. We used a spatially-explicit optimization algorithm to analyze the impacts of small-to-large scale biomass production by identifying locations that maximize biofuel produced from switchgrass and minimize negative impacts on biodiversity and agriculture. Results: Using CRP land for switchgrass production increases the land area required to meet biomass goals and the species range area altered for birds, amphibians, mammals, and reptiles. When conversion is not limited to CRP, conversion scenarios including biodiversity and agriculture trade-offs require greater than 100 % more area for switchgrass to reach the same production goals. When land conversion scenarios do not include biodiversity, twice the range area for reptiles and amphibians could be altered. Conclusions: Land-use trade-offs between biofuel production, agriculture, and biodiversity exist and alter optimum location of land conversion for low-to-high biofuel levels. This highlights the need for systematic land-use planning for the future. [ABSTRACT FROM AUTHOR]

Switchgrass ( Panicum virgatum L.) is a perennial warm-season grass identified as a model species for bioenergy feedstock production. Established switchgrass stands are very resilient to the environmental fluctuations; however, seed dormancy and weak seedling vigor make establishment difficult. Breaking seed dormancy of switchgrass is a first step to reduce risk of establishment failure and the costs associated with reseeding. Many studies have reported a myriad of methods to break seed dormancy of switchgrass, including chemical, mechanical, thermal, and hormonal seed treatments. Length of seed storage, storage conditions (e.g., temperature and humidity), and prior soil conditions (e.g., soil salinity and fertilizer rates) affect switchgrass seed dormancy. Strong interactions exist among germination, seedling emergence, and soil conditions; therefore, treated seeds tested in soil media will generate more accurate results following dormancy breaking techniques. This paper reviews the current methods used to break switchgrass seed dormancy. [ABSTRACT FROM AUTHOR]

Improvement and year-to-year stabilization of biomass yields are primary objectives for the development of a low-input switchgrass feedstock production system using microbial endophytes. An earlier investigation of the effect of Burkholderia phytofirmans strain PsJN on switchgrass germplasm demonstrated differential responses between genotypes. PsJN inoculation of cv. Alamo (lowland ecotype) increased the plant root system, shoot length, and biomass yields, whereas it had no beneficial effect on cv. Cave-in-Rock (upland ecotype). To understand the gene networks governing plant growth promotion responses triggered by PsJN, the gene expression profiles were analysed in these two hosts, following seedling inoculation. The Affymetrix platform switchgrass expressed sequence tag (EST) microarray chip representing 122 972 probe sets, developed by the DOE BioEnergy Science Center, was employed to assess transcript abundance at 0.5, 2,4, and 8 DAI (days after PsJN inoculation). Approximately 20 000 switchgrass probe sets showed significant responses in either cultivar. Switchgrass identifiers were used to map 19 421 genes in MapMan software. There were apparent differences in gene expression profiling between responsive and non-responsive cultivars after PsJN inoculation. Overall, there were 14 984 and 9691 genes affected by PsJN inoculation in Alamo and Cave-in-Rock, respectively. Of these, 394 are annotated as pathogenesis-related genes. In the responsive cv. Alamo, 68 pathogenesis-related genes were affected, compared with only 10 in the non-responsive cv. Cave-in-Rock. At the very early stage at 0.5 DAI, both cultivars exhibited similar recognition and defence responses, such as genes in signalling and proteolysis, after which the defence reaction in the responsive cv. Alamo became weaker while it was sustained in non-responsive cv. Cave-in-Rock. [ABSTRACT FROM AUTHOR]

Searching for novel energy crops, an interest in C4-type plant switchgrass (SWG) has increased worldwide. The present research was aimed to study SWG genetic resources for most important agrobiological traits with a view of extending the range of energy plants in the Nemoral zone of Europe. SWG was studied for the peculiarities of developmental stages, winter hardiness, and dry matter (DM) yield. SWG regrowth in spring started one month later compared to the reed canary grass (variety ‘Chiefton’). All investigated genotypes matured seeds in the second half of September. The most winter-hardy SWG accessions (0–20% winter damage) were the majority of wild ecotypes and the variety ‘Dacotah’ from North Dakota (2–4 hardiness zone) as well as the variety ‘Summer’ from South Nebraska (4, 5 hardiness zone). Ecotypes from North Dakota exhibited a high breeding potential and prospects in Northern regions of Europe due to genotypic variation of winter hardiness trait. The varieties ‘Alamo’, ‘Falcon’, ‘Grenville’, ‘Shawnee’, and ‘Trailblazer’ that originated from warmer climate zones (6–9 hardiness zone) were heavily damaged or completely killed. The worst overwinter survival of plants was recorded after the first winter. DM yield was estimated at two regimens of cutting. When grass was cut once at seed maturity stage, DM yield in the first harvest year was 249 g per plant, in the second harvest year 349 g per plant, and in the third harvest year 493 g per plant. When grass was cut twice per season (at the beginning of anthesis and after regrowth of aftermath), DM yield was significantly lower: in the first harvest year the DM yield was 203 g per plant (18.4% less), in the second harvest year 182 g per plant (47.9% less), and in the third harvest year 272 g per plant (44.7% less). [ABSTRACT FROM PUBLISHER]

Background: Switchgrass (Panicum virgatum L.) has a great potential as a platform for the production of biobased plastics, chemicals and energy mainly because of its high biomass yield on marginal land and low agricultural inputs. During the last decade, there has been increased interest in the genetic improvement of this crop through transgenic approaches. Since switchgrass, like most perennial grasses, is exclusively cross pollinating and poorly domesticated, preventing the dispersal of transgenic pollen into the environment is a critical requisite for the commercial deployment of this important biomass crop. In this study, the feasibility of controlling pollen-mediated gene flow in transgenic switchgrass using the large serine site-specific recombinase Bxb1 has been investigated. Results: A novel approach utilizing co-transformation of two separate vectors was used to test the functionality of the Bxb1/att recombination system in switchgrass. In addition, two promoters with high pollen-specific activity were identified and thoroughly characterized prior to their introduction into a test vector explicitly designed for both autoexcision and quantitative analyses of recombination events. Our strategy for developmentally programmed precise excision of the recombinase and marker genes in switchgrass pollen resulted in the generation of transgene-excised progeny. The autoexcision efficiencies were in the range of 22-42% depending on the transformation event and assay used. Conclusion: The results presented here mark an important milestone towards the establishment of a reliable biocontainment system for switchgrass which will facilitate the development of this crop as a biorefinery feedstock through advanced biotechnological approaches. [ABSTRACT FROM AUTHOR]

Key message: With a novel elite genotype, SA37, and an improved transformation protocol, it is now possible to routinely and efficiently engineer switchgrass using biolistic transformation. Abstract: Transformation of elite switchgrass ( Panicum virgatum L.) genotypes would facilitate the characterization of genes related to cell wall recalcitrance to saccharification. However, transformation of explants from switchgrass plants has remained difficult. Therefore, the objective of this study was to develop a biolistic transformation protocol for elite genotypes. Three switchgrass genotypes (ST1, ST2, and AL2) were previously selected for tissue culture responsiveness. One genotype, SA37, was selected for further use due to its improved formation of callus amenable to transformation. Various medium sets were compared and a previously published medium set provided cultures with >96 % embryogenic callus, and data on transient and stable gene expression of RFP were used to optimize biolistic parameters, and further validate the switchgrass ( PvUbi1) promoter. SA37 proved to be the most transformable, whereas eight transgenic calli on average were recovered per bombardment of 20 calli (40 % efficiency) when using a three-day day preculture step, 0.6 M osmotic adjustment medium, 4,482 kPa rupture disks and 0.4 μm gold particles which traveled 9 cm before hitting the target callus tissue. Regenerability was high, especially for ST2, for which it is possible to recover on average over 400 plants per half-gram callus tissue. It is now possible to routinely and efficiently engineer elite switchgrass genotypes using biolistic transformation. [ABSTRACT FROM AUTHOR]

Our understanding of how mineral nutrition affects productivity and composition of bioenergy crops grown on marginal lands remains fragmented and incomplete despite world-wide interest in using herbaceous biomass as an energy feedstock. Our aim was to determine switchgrass ( Panicum virgatum L.) biomass production and maize ( Zea mays L.) grain yield on marginal soils used previously to evaluate the effect of soil phosphorus (P) and potassium (K) fertility on alfalfa ( Medicago sativa L.) forage production. Grain yield of maize was reduced on P- and/or K-limited plots that also impaired alfalfa forage yield, whereas switchgrass biomass yields were high even in plots possessing very low available P (4 mg kg-1) and K (< 70 mg kg-1) levels. Linear-plateau regression models effectively described the relationship of soil test P and K to tissue P and K concentrations, and tissue P and K concentrations accurately predicted removal of P and K in harvest biomass. However, neither soil-test P and K, nor tissue P and K concentrations were effective as diagnostics for predicting switchgrass biomass yield nor could soil tests and their change with cropping predict nutrient removal. Concentrations of cellulose, hemicellulose, lignin, and ash were not influenced by P and K nutrition. Predicted bio-ethanol production was closely associated with biomass yield whereas high biomass K concentrations reduced estimated bio-oil production per hectare by as much as 50%. Additional research is needed to identify diagnostics and managements to meet the bioenergy production co-objectives of having high yield of biomass with very low mineral nutrient concentrations (especially K) while sustaining and improving the fertility of marginal soils. [ABSTRACT FROM AUTHOR]

Although upgrading bio-oil from fast pyrolysis of biomass is an attractive pathway for biofuel production, nitrogen (N) and mineral matter carried over from the feedstock to the bio-oil represents a serious contaminant in the process. Reducing the N and ash content of biomass feedstocks would improve process reliability and reduce production costs of pyrolytic biofuels. This study investigated: (1) How does switchgrass harvest date influence the yield, N concentration ([N]), and ash concentration of biomass and fast pyrolysis products? and (2) Is there a predictive relationship between [N] of switchgrass biomass and [N] of fast pyrolysis products? Switchgrass from five harvest dates and varying [N] from central Iowa were pyrolyzed using a free-fall reactor. Harvestable biomass peaked in August (8.6 Mg ha), dropping significantly by November (6.7 Mg ha, P = 0.0027). Production of bio-oil per unit area mirrored that of harvested biomass at each harvest date; however, bio-oil yield per unit dry biomass increased from 46.6 % to 56.7 % during the season ( P = 0.0018). Allowing switchgrass to senesce lowered biomass [N] dramatically, by as much as 68 % from June to November ( P < 0.0001). Concurrently, bio-oil [N] declined from 0.51 % in June to 0.17 % by November ( P < 0.0001). Significant reductions in ash concentration were also observed in biomass and char. Finally, we show for the first time that the [N] of switchgrass biomass is a strong predictor of the [N] of bio-oil, char, and non-condensable gas with R values of 0.89, 0.94, and 0.88, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Two field experiments were conducted, one each with the energy grasses switchgrass, Panicum virgatum L. and reed canary grass, Phalaris arundinacea L., to determine the role of nutritional elements in optimizing crop yield and associated effects on crop quality for thermal energy conversion technologies. The two experiments were adjacent and on low productivity sandy soils in the South East of England. This paper reports the crop yield effects during the years 2003–2005. Nitrogen was added in 50 kg ha−1 increments from 0 to 250 kg ha−1 Nitrogen. The Potassium and Sulphur treatments were applied in combination with 50 and 150 kg ha−1 Nitrogen. No yield increase was detected, suggesting that the soil Potassium and Sulphur supply was already sufficient. In reed canary grass a yield response was recorded when 50 kg ha−1 Nitrogen was applied. However, the greater statistical power achieved by pooling the Potassium and Sulphur treatments at the 2 rates of Nitrogen showed that application of 150 kg ha−1 Nitrogen compared to 50 kg ha−1 Nitrogen, to reed canary grass, increased crop yield in each of the three years of the study, and by a maximum of 1.35 t ha−1 Dry Matter in 2004. The same comparison in switchgrass showed a lesser response (0.7 t ha−1 Dry Matter) to 150 compared to 50 kg ha−1 Nitrogen and in one year only (2003). Therefore, the data generally show reed canary grass to be the more responsive crop to nitrogen, but all data should be viewed in respect of the limitations to yield imposed by site conditions. For both crops, yield peaked in either late summer or early autumn and then declined overwinter, most markedly in 2004–05. Overall, mean crop yield at final harvest for both crops, in late winter of each year, was low (<4 t ha−1 Dry Matter). This was considered to be due to water stress. The sandy soils had a low water holding capacity and the weather during 2003–05 was generally warmer and dryer than the long term average for the site. Block 3 of the reed canary grass experiment rooted into an area of finer textured soil (at ca. 1.5 m depth) and produced greater yields (5.45 cf. 3.25 and 3.01 t ha−1 Dry Matter) from Blocks 1 and 2 respectively in 2004–05. The results clearly indicate that these genotypes of switchgrass and reed canary grass may fail to give financially viable yields on inherently low productivity sites, and that varieties specially selected for such conditions will need to be bred for the industry if such areas are to be used. [Copyright &y& Elsevier]

Abstract: To better understand the ability of switchgrass (Panicum virgatum L.), a perennial grass often relegated to marginal agricultural areas with minimal inputs, to remove cadmium, chromium, and zinc by phytoextraction from contaminated sites, the relationship between plant metal content and biomass yield is expressed in different models to predict the amount of metals switchgrass can extract. These models are reliable in assessing the use of switchgrass for phytoremediation of heavy-metal-contaminated sites. In the present study, linear and exponential decay models are more suitable for presenting the relationship between plant cadmium and dry weight. The maximum extractions of cadmium using switchgrass, as predicted by the linear and exponential decay models, approached 40 and 34μgpot−1, respectively. The log normal model was superior in predicting the relationship between plant chromium and dry weight. The predicted maximum extraction of chromium by switchgrass was about 56μgpot−1. In addition, the exponential decay and log normal models were better than the linear model in predicting the relationship between plant zinc and dry weight. The maximum extractions of zinc by switchgrass, as predicted by the exponential decay and log normal models, were about 358 and 254μgpot−1, respectively. To meet the maximum removal of Cd, Cr, and Zn, one can adopt the optimal timing of harvest as plant Cd, Cr, and Zn approach 450 and 526mgkg−1, 266mgkg−1, and 3022 and 5000mgkg−1, respectively. Due to the well-known agronomic characteristics of cultivation and the high biomass production of switchgrass, it is practicable to use switchgrass for the phytoextraction of heavy metals in situ. [Copyright &y& Elsevier]

Abstract: Six treated lignocellulosic samples from three feedstocks (switchgrass, corn stover, and anaerobically digested manure fiber) under two pretreatment methods (alkali and acid treatments) were used to culture Trichoderma reesei Rut C-30. Effects of treated lignocellulosic materials on fungal cellulase/xylanase production and corresponding hydrolysis were elucidated. The results demonstrated that the cultures on alkali treated samples had better enzyme production than the acid treated samples. The consequent hydrolysis indicated that with the same feedstock and hydrolysis conditions, enzymes from cultures on different treated samples had significantly different hydrolysis performance compared to commercial enzymes and enzymes from cultures on chemical defined medium. The statistical comparison further demonstrated that enzymes from cultures on alkali and acid treated lignocellulosic materials were favorable to hydrolyze the corresponding groups of the treated materials. [Copyright &y& Elsevier]

Lignin content of switchgrass ( Panicum virgatum L.), a bioenergy species, is a critical determinant of biomass quality since it can negatively impact conversion of biomass into liquid fuels via biochemical platforms. Cinnamyl alcohol dehydrogenase (CAD) is a key enzyme in lignin biosynthesis. Here, we have shown that cv. Kanlow switchgrass contains at least two closely related CAD genes ( PviCAD1 and PviCAD2) that code for proteins containing highly conserved domains and residues that identify them as bona fide CADs. Both recombinant proteins displayed substrate kinetics consistent with their presumed role in cell wall lignification. Proteomic and immunoblotting detected CAD containing spots in internode protein extracts, and proteomic analyses demonstrated that both CADs were expressed. In planta CAD activity, CAD protein levels were observed at all stages of tiller development. A real-time qPCR analysis of the two CADs and one CAD-like sequence indicated that transcripts coding for PviCAD1 were present in greater abundance than those coding for PviCAD2. Transcripts for a third CAD-like sequence ( PviAroADH) were present at intermediate levels as compared to PviCAD1 and CAD2. The predicted protein sequence of PviAroADH indicated that it was an enzyme unrelated to lignification based on phylogenetic and protein modeling data. [ABSTRACT FROM AUTHOR]

Abstract: Four populations of switchgrass (Alamo, GA993, GA992, Kanlow), Panicum virgatum L., were studied for the difference of their chemical constituents. The extractives, Klason lignin, and carbohydrates compositions of the stem portion of these switchgrass populations were determined by gas chromatography mass spectroscopy (GC-MS) and high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) respectively. Ball milled grass lignin (BMGL) was isolated and analyzed by NMR spectroscopy. The results demonstrated that the chemical compositions of four switchgrass populations were similar with the exception of the lignin content and chemical composition of extractives. The results of quantitative 13C NMR spectroscopy indicated that switchgrass lignin consisted of p-hydroxylphenyl, guaiacyl, and syringyl units in an average ratio of 26:42:32 and incorporated with p-coumaric acid and ferulic acid at a level of approximately 0.20 per aromatic ring. The lignin structure of four switchgrass cultivars was comparable. [Copyright &y& Elsevier]

Information on the genetic variability of seed yield and yield components is limited and no information is available on correlations among seed yield and yield components and direct and indirect effects of the yield components on seed yield in switchgrass, Panicum virgatum L. Accordingly, we conducted replicated experiments at Chickasha and Perkins, OK, in 1998 involving 11 lowland type switchgrass populations to assess genetic variation for seed yield and yield components, quantify interrelationships among them, and determine direct and indirect effects of yield components on seed yield through path coefficient analysis to identify traits for indirect selection of seed yield. Significant ( P ≤ 0.01) variation existed among the 11 populations over locations for percent seed set and 100-seed weight. Seed yield/plant and the seed yield components panicle number/plant, spikelet number/panicle, and seed number/panicle had significant ( P ≤ 0.05) population × location interactions, indicating substantial environmental influence on these traits for these populations. Accordingly, data for these traits were analyzed separately for each location revealing significant ( P ≤ 0.01) differences among populations at both locations for each of these traits. Phenotypic correlation between seed yield/plant and seed number/panicle was positive ( r = 0.76** at Chickasha and r = 0.72** at Perkins). Path coefficient analyses revealed that seed number/panicle had the highest positive direct effect on seed yield at both locations. Ample genetic variability was present among the switchgrass populations studied to allow breeding improvement of seed yield. Selection for increased seed number/panicle would be the most effective means of indirectly selecting for higher seed yield within this germplasm. Correlation and path coefficient analyses among biomass yield, seed yield, and harvest index indicated that, at least within the switchgrass germplasm studied, it would be possible to breed switchgrass cultivars with enhanced biomass yielding ability and sufficient seed production capability for their commercial propagation. [ABSTRACT FROM AUTHOR]

Abstract: Perennial warm season grasses, such as switchgrass (Panicum virgatum L.), complement cool-season species by filling the period of low biomass production called summer-slump. Although switchgrass is widespread in the Great Plains of the USA, there is very little information available about its management in mountain regions. A field experiment was conducted in Blacksburg, VA, USA, to determine the influence of dates of first and regrowth harvest, and cutting height on the canopy structure of the winter hardy cv. ‘Pathfinder’. The number, height and weight of tillers, yield distribution, light penetration through the canopy, leafiness, specific leaf area and leaf area index were investigated. Harvested biomass yield increased as date of first harvest was delayed throughout June and cutting height was reduced from 300mm to 200mm, but the yield of regrowth declined accordingly. This decline was caused by the removal of an increasing percentage of apical meristems and increasing damage to the crop canopy, in particular the loss of a greater proportion of photosynthetically active leaf area. A lower cutting height also reduced the amount of biomass produced in the following year. Cutting at 300mm in early June can maximise the amount of high quality (defined as high concentrations of in vitro digestible dry matter and crude protein) biomass available for use as animal feed as compensation for cool season grasses during the first half of July. [Copyright &y& Elsevier]

Abstract: Alfalfa stems, reed canarygrass, and switchgrass; perennial herbaceous species that have potential as biomass energy crops in temperate regions; were evaluated for their bioconversion potential as energy crops. Each forage species was harvested at two or three maturity stages and analyzed for carbohydrates, lignin, protein, lipid, organic acids, and mineral composition. The biomass samples were also evaluated for sugar yields following pretreatment with dilute sulfuric followed by enzymatic saccharification using a commercial cellulase preparation. Total carbohydrate content of the plants varied from 518 to 655gkg−1 dry matter (DM) and cellulose concentration from 209 to 322gkg−1 DM. Carbohydrate and lignin contents were lower for samples from early maturity samples compared to samples from late maturity harvests. Several important trends were observed in regards to the efficiency of sugar recovery following treatments with dilute acid and cellulase. First, a significant amount of the available carbohydrates were in the form of soluble sugars and storage carbohydrates (4.3–16.3% wt/wt). Recovery of soluble sugars following dilute acid pretreatment was problematic, especially that of fructose. Fructose was found to be extremely labile to the dilute acid pretreatments. Second, the efficiency at which available glucose was recovered was inversely correlated to maturity and lignin content. However, total glucose yields were higher for the later maturities because of higher cellulose contents compared to the earlier maturity samples. Finally, cell wall polysaccharides, as determined by the widely applied detergent fiber system were found to be inaccurate. The detergent fiber method consistently over-estimated cellulose and hemicellulose and underestimated lignin by substantial amounts. [Copyright &y& Elsevier]

Abstract: Biomass tensile and shear ultimate failure stresses were measured with the aim of identifying biomass “weakest mode of failure” or “natural fracture point” as a basis for future grinder designs. Switchgrass (Panicum virgatum L.) ultimate stresses were determined for Alamo and Kanlow varieties over ranges in maturity and moisture content. Alamo had greater ultimate tensile stress than Kanlow (), with mean values of 97.8 and 89.7MPa, respectively. Alamo had greater ultimate shear stress than Kanlow (), with mean values of 20.5 and 17.9MPa, respectively. Shear was the “weakest mode of failure”. Grinders that use knives, shear bars, and mechanical pinch points that apply opposed-sliding actions are expected to be more energy efficient. Mean ultimate tensile stress and shear stress were significantly different between switchgrass varieties. A survey of failure stresses for a range of biomass feedstocks is recommended for future study. Ultimate tensile stress increased two-fold as elapsed time after harvest increased from 2 to 386h, with a corresponding (confounded) decrease in moisture content of ∼60–10% (wet basis (w.b.)). Future study should isolate whether the effect was due primarily to moisture or aging. Tensile-dominant size reduction should be conducted early in the harvest process and at a high moisture content to minimize energy consumption for grinding. Ultimate shear stress was relatively insensitive to switchgrass maturity, elapsed time after harvest, and moisture content. [Copyright &y& Elsevier]

Abstract: Switchgrass (Panicum virgatum L.) is considered a good biofuels feedstock candidate. However, limited information is available on its productivity and harvest management in the upper southeastern USA. Our objective was to examine production potential of upland and lowland switchgrass cultivars in response to one- or two-cut management across the region. Upland (‘Cave-in-Rock’ and ‘Shelter’) and lowland (‘Alamo’ and ‘Kanlow’) cultivars were harvested for 3yr under one- or two-cut management at eight sites in five states (North Carolina, Kentucky, Tennessee, Virginia, and West Virginia). Across all sites, years, and cutting managements, upland cultivars yielded 12.6 vs. 15.8Mgha−1 for lowland cultivars. Both cultivars yielded more on average with two harvests rather than one, but the effect was greater for upland cultivars (36% more biomass), while lowland cultivars yielded only 8% more biomass with two harvests. Tiller densities were higher for Alamo (lowland) than for Cave-in-Rock (upland) and higher with two-cut than with one-cut management. Early season production of Alamo (a cultivar of southern origin) appeared sensitive to low temperatures. Weak linear responses to precipitation were observed for first-cut biomass, but none was observed for summer precipitation. Lowland switchgrass cultivars appear better suited to biomass production in the upper southeastern USA, due to their greater productivity. Two vs. one cutting per year may be of less advantage for biomass yield with lowland cultivars in this region. However, if upland cultivars are used, two harvests may be of benefit dependent upon production costs and feedstock quality. [Copyright &y& Elsevier]

Abstract: Limited information is available regarding biomass production potential of long-term (>5-yr-old) switchgrass (Panicum virgatum L.) stands. Variables of interest in biomass production systems include cultivar selection, site/environment effects, and the impacts of fertility and harvest management on productivity and stand life. We studied biomass production of two upland and two lowland cultivars under two different managements at eight sites in the upper southeastern USA during 1999–2001. (Sites had been planted in 1992 and continuously managed for biomass production.) Switchgrass plots under lower-input management received 50kgNha−1 yr−1 and were harvested once, at the end of the season. Plots under higher-input management received 100kgNha−1 (in two applications) and were harvested twice, in midsummer and at the end of the season. Management effects on yield, N removal, and stand density were evaluated. Annual biomass production across years, sites, cultivars, and managements averaged 14.2Mgha−1. Across years and sites, a large (28%) yield response to increased inputs was observed for upland cultivars; but the potential value of higher-input management for lowland cultivars was masked overall by large site×management interactions. Nitrogen removal was greater under the higher-input system largely due to greater N concentrations in the midsummer harvests. Management recommendations (cultivar, fertilization, and harvest frequency), ideally, should be site and cultivar dependent, given the variable responses reported here. [Copyright &y& Elsevier]

An efficient and reproducible in vitro culture system has been developed for regeneration of multiple shoot clumps from intact seedlings of both lowland and upland cultivars of switchgrass ( Panicum virgatum L.). The multiple shoots were induced on Murashige and Skoog medium supplemented with various combinations of 2,4-dichlorophenoxyacetic acid (2,4-D) and 1-phenyl-3-(1,2,3-thiadiazol-5YL)-urea (thidiazuron or TDZ). Maximum response was obtained with 4.5 μ M 2,4-D and 18.2 μ M TDZ. These shoots proliferated and rooted efficiently on MS medium without growth regulators. The developmental pattern of the multiple shoots indicated their origin from the enlarged shoot apex via proliferation of axillary buds and subsequent reprogramming of shoot meristems followed by secondary differentiation of adventitious shoots The simplicity of the protocol and direct production of multiple shoots make this a potential system that is highly attractive and amenable for microprojectile-mediated gene transfer. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass is one of the dominant renewable energy resources suited for the production of sustainable biofuels and other energy purposes. This study was focused on weed management strategies that can improve the establishment of six lignocellulosic crops. The studied crops included: giant miscanthus, switchgrass, giant reed, cardoon, sweet sorghum, and kenaf. Delayed planting, increased planting densities, and mulching techniques can suppress weeds in giant miscanthus. Weed competition is detrimental for switchgrass establishment. Seedbed preparation and cultivar selection can determine its ability to compete with weeds. Giant reed is unlikely to get outcompeted by weeds, and any weed control operation is required only for the first growing season. Competitive cultivars and increased seeding rates maximize the competitiveness of cardoon against weeds. Several cultural practices can be used for non-chemical weed management in sweet sorghum and kenaf. For all crops, pre-emergence herbicides can be applied. The available safe post-emergence herbicides are limited. Mechanical weed control during crucial growth stages can provide solutions for sweet sorghum, kenaf, and perennial grasses. Further research is required to develop effective weed management strategies, with emphasis on cultural practices, that can improve the establishment of these prominent lignocellulosic crops. [ABSTRACT FROM AUTHOR]